Problems loading a style css from another directory

Hello!
Today I load a css dynamically as follows:

PHP Code:

   function addStyle($file = '')
    {
        $ci = &get_instance();
        $header_css = $ci->config->item('header_css');

        if (empty($file) || !$file) {
            return;
        }

        if (is_array($file)) {
            foreach ($file as $item) {
                $header_css[] = $item;
            }

            $ci->config->set_item('header_css', $header_css);
        } else {
            $header_css[] = $file;
            $ci->config->set_item('header_css', $header_css);
        }
    } 


This works fine, but when I try to load into another directory, the function can not find the style, causing error.
Does anyone know of any way to dynamically load the css being able to be in another directory as well?

Thank you!